1. Field of the Invention
The present invention relates to a DCxe2x80x94DC converter and, more particularly, a DCxe2x80x94DC converter constructed such that a power consumed in the converter can be reduced in the state that a load applied to the converter is a light load and a driving method for the same.
2. Description of the Related Art
As is well known, the DCxe2x80x94DC converter functions to convert the input DC voltage into the different DC voltage, and is often used as the driving power supply for the DC driving circuit having the relatively light load. The output voltage of this DCxe2x80x94DC converter must be stabilized to the predetermined voltage value, and also the consumption power in the converter must be reduced as small as possible if the case that such DCxe2x80x94DC converter is installed into the mobile terminal, etc. is considered.
By the way, recently the organic EL display that employs the organic EL element as the light emitting source, for example, is watched with interest as the display means used in the above mobile terminal, etc. and there is a tendency to utilize this display. In order to lighten/drive the above organic EL element, normally the DC voltage of about 10 to 20 V is required. Therefore, in the case that this organic EL display is utilized in the mobile terminal or the vehicle equipment, the driving voltage value is insufficient and thus the driving voltage must be increased by the DCxe2x80x94DC converter.
In contrast, the output current of the DCxe2x80x94DC converter is largely varied according to the lighting state of the organic EL display. For example, the consumption current becomes large if the number of the lighted pixels is large and the lightening brightness at that time is high, while the consumption current becomes small if the number of the lighted pixels is small and the lightening brightness at that time is low.
FIG. 5 shows an example of the step-up type DCxe2x80x94DC converter that is employed preferably in the case that the above organic EL display is used as the load, for example. In FIG. 5, a symbol Vin denotes a power-supply input terminal of the DCxe2x80x94DC converter, i.e., a terminal to which the voltage that is fed from the primary battery, etc. is supplied. The coil L1 is connected to the input terminal Vin, the diode D1 is connected in parallel with the coil L1, and the cathode side of the diode D1 constitutes the output terminal Vout. Then, the voltage holding capacitor C1 is connected between the output terminal Vout and the reference potential point (earth). The output voltage of the converter, which is held by the capacitor C1, is supplied to the load 10.
The voltage divider circuit 11, which consists of the resistor R1 and the resistor R2 to detect the output voltage of the converter, is connected between the output terminal Vout and the earth. The detected voltage generated by this voltage divider circuit 11 is supplied to one input terminal of the error amplifier 13 constituting the error detecting circuit. Also, the reference voltage generated in the reference voltage generating circuit 12 is supplied to the other input terminal of the error amplifier 13, so that the error output signal that is generated pursuant to the variation of the output voltage of the converter is output from the error amplifier 13.
The error output signal generated by the error amplifier 13 is supplied to the regulator circuit 14 constituting the output voltage adjusting circuit. The gate terminal of the n-type MOSFET Q1 serving as the switching element is connected to the output terminal of this regulator circuit 14. Also, the drain terminal of the FET Q1 is connected to the coil L1 on the output terminal Vout side, and the source terminal thereof is grounded. Also, the reference clock signal that is fed from the reference clock generating circuit 15 is supplied to the regulator circuit 14.
In addition, the operating power supply is supplied to the output voltage controlling means that controls the output voltage of the converter in the predetermined range, i.e., the voltage divider circuit 11, the reference voltage generating circuit 12, the error amplifier 13, and the regulator circuit 14, from the input terminal Vin and the output terminal Vout respectively.
In the above circuit configuration, if the FET Q1 is turned ON by the control signal (switching signal) from the regulator circuit 14, the current flows to the coil L1 from the input terminal Vin and thus the electromagnetic energy is accumulated in the coil L1. Then, if the FET Q1 is turned OFF, the electromotive force is generated in the coil L1 by the energy accumulated in the coil L1 and thus the current flows via the diode D1. Therefore, the voltage at the output terminal Vout is caused to increase. As a result, the voltage that is higher than that at the input terminal Vin generated at the output terminal Vout.
In the above DCxe2x80x94DC converter, normally two methods are known as the control method that maintains the output voltage in the almost constant range. One is the PWM (Pulse Width Modulation) system, and the other is the PFM (Pulse Frequency Modulation) system. The former PWM system controls to change the ON-time of the FET Q1 serving as the switching element based on the difference between the voltage that is the divided voltage of the output voltage (detected voltage) and the reference voltage. That is, if the difference is large in the state of the reference voltage greater than the detected voltage, the time during which the FET Q1 is turned ON is controlled to extend. Accordingly, the electromagnetic energy accumulated in the coil L1 is increased and consequently the detected voltage is controlled such that such voltage is made equal to the reference voltage. Thus, the output voltage of the converter is controlled to stay in the predetermined range.
On the contrary, the latter PFM system sets the ON-time of the above FET Q1 constant, and then controls such that the step-up operation is carried out by turning ON the FET Q1 periodically if the difference is in the state of the reference voltage greater than the detected voltage while the step-up operation is not carried out by stopping the ON-operation of the switching element Q1 temporarily if the difference become the state of the reference voltagexe2x89xa6the detected voltage. As a result, the detected voltage is controlled such that such detected voltage can be set equally to the reference voltage, and thus the output voltage of the converter can be controlled within the predetermined range. If any system is employed, the timing to start the step-up operation (ON-operation of the switching element Q1) can be set by the reference clock that is supplied by the above reference clock generating circuit 15.
Meanwhile, as described above, in the DCxe2x80x94DC converter of this type, the operating power supply is always supplied to the output voltage controlling means that controls the output voltage of the converter in the predetermined range, i.e., the voltage divider circuit 11, the reference voltage generating circuit 12, the error amplifier 13, and the regulator circuit 14, from the input terminal Vin and the output terminal Vout respectively, and respective circuits are driven by this operating power supply. In other words, it is understood that the output voltage controlling means consisting of above respective circuits always consumes the power in the middle of the operation of the DCxe2x80x94DC converter.
Therefore, in the case that the organic EL display panel that is driven by the output voltage of the above DCxe2x80x94DC converter is considered, if the number of the lighted pixels is small and the lightening brightness at that time is low, the consumption current is very small. As a result, such a situation is brought about that the power consumed in the above output voltage controlling means of the DCxe2x80x94DC converter is in excess of the power consumed in the emission of the display panel. Although depending upon various conditions, sometime the power consumed in the output voltage controlling means of the above converter becomes several time to several tens times the power required to drive the display panel.
As described above, in the above DCxe2x80x94DC converter having the conventional configuration, the predetermined power is always consumed in the output voltage controlling means of the above converter irrespective of the level of the output power supplied from the converter. Thus, in the case that the output power supplied to the load is small, the power consumed in the output voltage controlling means of the above converter accounts for a high rate of the consumption power in the load. In other words, the dead power that does not contribute to drive the load is consumed in the converter.
The present invention has been made in view of the above problem, and it is an object of the present invention to provide a DCxe2x80x94DC converter constructed such that a power consumed in the converter can also be reduced in the case that a power consumed in a load is small (in the case of light load) to thereby improve a power utilization efficiency and a driving method for the same.
In order to achieve the above object, a DCxe2x80x94DC converter according to the present invention having an output voltage controlling means for getting an output voltage of a converter and then controlling the output voltage of the converter within a predetermined range based the voltage, comprises an operating power supply supplying means for supplying an operating power supply, which operates the output voltage controlling means, intermittently to the output voltage controlling means.
In this case, preferably the output voltage controlling means is constructed by a voltage divider circuit for detecting the output voltage of the converter, a reference voltage generating circuit, an error detecting circuit for generating an error output signal by comparing a detected voltage generated by the voltage divider circuit with a reference voltage generated by the reference voltage generating circuit, and an output voltage adjusting circuit for adjusting the output voltage of the converter based on the error output signal generated by the error detecting circuit.
Then, in one preferred embodiment, the operating power supply supplying means is constructed to supply intermittently the operating power supply to any circuit of the voltage divider circuit, the reference voltage generating circuit, the error detecting circuit, and the output voltage adjusting circuit.
Also, in another preferred embodiment, the operating power supply supplying means is constructed to stop simultaneously supply of the operating power supply to plural circuits out of the voltage divider circuit, the reference voltage generating circuit, the error detecting circuit, and the output voltage adjusting circuit and to supply simultaneously the operating power supply to the plural circuits.
Further, in other preferred embodiment, the operating power supply supplying means is constructed to stop simultaneously supply of the operating power supply to the voltage divider circuit, the reference voltage generating circuit, the error detecting circuit, and the output voltage adjusting circuit and to supply simultaneously the operating power supply to respective circuits.
Then, in above embodiments, the operating power supply supplying means is constructed to execute a driving operation of a switching element, which controls the output voltage of the converter based on the error output signal fed from the error detecting circuit, and to stop supply of the operating power supply fed from the operating power supply supplying means in response to a period of a driving operation of the switching element.
In this case, preferably the DCxe2x80x94DC converter further comprises a timing generating circuit for detecting the period of the driving operation of the switching element; wherein the timing generating circuit is constructed to stop supply of the operating power supply fed from the operating power supply supplying means in response to the period of the driving operation of the switching element.
Also, it is desired that the timing generating circuit is constructed to change a supply stop period of the operating power supply fed from operating power supply supplying means in response to the period of the driving operation of the switching element.
In addition, it is desired that the timing generating circuit is constructed to cause switching means, which constitute the operating power supply supplying means, to execute an ON/OFF operation by using a reference clock that manages a driving timing of the switching element.
Also, a control signal indicating a load state in a load circuit, which utilizes the output voltage of the converter, is further supplied to the timing generating circuit, and the timing generating circuit is constructed to control the ON/OFF operation of the switching means, which constitute the operating power supply supplying means, in response to the control signal indicating the load state.
Also, it is desired that the timing generating circuit is constructed to ON-control the switching means, which constitute the operating power supply supplying means, by using the reference clock before the ON/OFF operation of the switching means is executed and to supply the operating power supply to the output voltage controlling means.
Then, a current is supplied to a coil from a DC power supply on a primary side by an ON operation of the switching means to execute an operation for accumulating an electromagnetic energy, and the energy accumulated in the coil is discharged by an OFF operation of the switching means to increase the output voltage.
In addition, a switching driving signal supplied from the output voltage adjusting circuit to the switching means is a switching driving signal that is modulated by a PFM system or a PWM system.
Meanwhile, in order to achieve the above object, a DCxe2x80x94DC converter driving method of the present invention of driving a DCxe2x80x94DC converter that has an output voltage controlling means for getting an output voltage of a converter and then controlling the output voltage of the converter within a predetermined range based the voltage, comprises the step of supplying an operating power supply, which operates the output voltage controlling means, intermittently to the output voltage controlling means.
In this case, in one preferred driving method, the operating power supply is supplied intermittently to any circuit out of a voltage divider circuit for detecting the output voltage of the converter, a reference voltage generating circuit, an error detecting circuit for generating an error output signal by comparing a detected voltage generated by the voltage divider circuit with a reference voltage generated by the reference voltage generating circuit, and an output voltage adjusting circuit for adjusting the output voltage of the converter based on the error output signal generated by the error detecting circuit, which constitute the output voltage controlling means.
Also, in another preferred driving method, supply of the operating power supply to plural circuits out of a voltage divider circuit for detecting the output voltage of the converter, a reference voltage generating circuit, an error detecting circuit for generating an error output signal by comparing a detected voltage generated by the voltage divider circuit with a reference voltage generated by the reference voltage generating circuit, and an output voltage adjusting circuit for adjusting the output voltage of the converter based on the error output signal generated by the error detecting circuit, which constitute the output voltage controlling means, is stopped simultaneously, and also the operating power supply to the plural circuits is supplied simultaneously.
Further, in other preferred driving method, supply of the operating power supply to a voltage divider circuit for detecting the output voltage of the converter, a reference voltage generating circuit, an error detecting circuit for generating an error output signal by comparing a detected voltage generated by the voltage divider circuit with a reference voltage generated by the reference voltage generating circuit, and an output voltage adjusting circuit for adjusting the output voltage of the converter based on the error output signal generated by the error detecting circuit, which constitute the output voltage controlling means, is stopped simultaneously, and also the operating power supply to respective circuits is supplied simultaneously.
Then, if any of above driving methods is employed, preferably an operating power supply supplying means for supplying intermittently an operating power supply that operates the output voltage controlling means is provided, and the operating power supply supplying means is constructed to decide a supply timing of the operating power supply in response to a control operation of the output voltage of the converter by the output voltage controlling means.
In addition, it is desired that an operating power supply supplying means for supplying intermittently an operating power supply that operates the output voltage controlling means is provided, and the operating power supply supplying means is constructed to decide a supply timing of the operating power supply by a control signal indicating a load state in a load circuit that uses the output voltage of the converter.
According to the DCxe2x80x94DC converter employing the above driving method, the output voltage adjusting circuit that controls the output voltage of the converter in the predetermined range is controlled by the error output signal fed from the error detecting circuit, and drives the switching elements in synchronism with the reference clock signal fed from the reference clock generating circuit. Therefore, the output voltage of the converter can be controlled in the predetermined range.
While, the signal indicating the driving state of the switching elements is supplied from the output voltage adjusting circuit to the timing generating circuit. The timing generating circuit can grasp the period of the driving operation of the switching elements, and then the operation for stopping the supply of the operating power supply to the output voltage controlling means is carried out by opening the switching elements, which constitute the operating power supply supplying means, if the period is longer than the predetermined period.
That is, if the period of the driving operation of the switching means is longer than the predetermined period, it can be decided that the load is set in the light state. In this case, in the period during when it is not required to execute the driving operation of the switching elements, there is no necessity that other circuits containing the output voltage adjusting circuit that drives the switching elements should be operated continuously. Therefore, the power supplied to respective circuits of the output voltage controlling means can be stopped temporarily in the above period by opening the switching means, which constitute the operating power supply supplying means. As a result, the utilization efficiency of the power in the light load situation can be improved.
In the case that the above control is carried out, the supply of the operating power supply to any circuit out of the voltage divider circuit, the reference voltage generating circuit, the error detecting circuit, and the output voltage adjusting circuit, which constitute the output voltage controlling means, may be temporarily stopped. Also, the supply of the operating power supply to all circuits may be temporarily stopped.
In addition, if the above timing generating circuit controls such that the period of the driving operation of the switching elements is grasped and then the supply stopping period of the operating power supply is changed in response to the period of the driving operation of the switching elements, the utilization efficiency of the power can be improved. Also, if the timing generating circuit is constructed to introduce the control signal indicating the load state, the load varying situation can be grasped previously not to depend on the control operation of the output voltage by the above output voltage controlling means. As a result, if this means is employed, the output voltage of the converter can be managed in the predetermined range particularly in the circumstances that the load is abruptly varied.